1. Field of the Invention
The present invention relates to an image producing method which is effective for expression of a gradient and, more particularly, to an image producing method for producing a picture image using a plurality of kinds of microdots having different densities.
The present invention also relates to a color image reproducing method for reproducing a color picture image using colorants of a plurality of colors and, more particularly, to a color image reproducing method using a plurality of colorants in which at least one color among a plurality of colors has different coloring densities.
An ink-jet printer will be described hereinbelow as an example of the apparatuses to realize such methods. However, it will be clear that the present invention can be applied even to image producing apparatuses of other types such as a printer of the thermal transfer copying type, or an electrophotographic printer, or the like.
2. Brief Description of Related Art
There has been proposed so far an image producing method for deriving a gradient by using a plurality of kinds of microdots having different densities (or "concentrations") and controlling the size of each dot. According to such a method, it is possible to express a gradient which cannot be expressed when dots of only one density are used. However, at the boundary portion between the dots having different densities, even if reflection optical densities of the thick dot and thin dot have been almost equally set, the difference in quality feeling due to the difference between the densities which are peculiar to those dots can be visually sensed, so that this results in a false profile and causes picture quality deteriorate.
On the other hand, a color picture image is generally reproduced using three colors which are for example, cyan, magenta and yellow, or using four colors which are such three colors and black in addition. Recently, there has been proposed a method whereby a plurality of colorants in which one color has different coloring densities are used for the purpose of enhancement of a color reproduction range.
In case of using two thick and thin colorants, a reproduction density range is remarkably enhanced since the colorants are changed over and are used in accordance with a reproduction density.
However, even in case of such a color picture image, there can occur similarly, but less noticeably, a difference in quality feeling among the microdots to be produced by the thick and thin colorants at the switching portions of the colorants, so that a so-called false profile is produced at this portion, which causes the quality of a reproduced picture image to deteriorate.